Multi-functional articles, in which multiple structural and/or functional materials, or components, are integrated to achieve advantages of reduced volume, area, weight, power consumption & management, cost, enhanced performance, and more are of great technological interest in many fields.
Multifunctional articles may combine PV cells and RF antennas, for example. The fields of PV cells and RF antenna are extensively documented. Systems incorporating both PV cells and RF antenna have also been described. PV cells are typically comprised of a layer of semi-conductor absorber material, a p-n junction and electrical contact layers for extracting current for external use or electrical storage. Exemplary absorber materials include crystalline Si and thin film, amorphous Si, CdTe or Cu—In—Ga—Se (CIGS). Thin film cells have been fabricated on flexible metal foils and polymeric sheets, which enable lightweight and flexible modules. In operation, PV cells are typically oriented towards the sun. In some systems, PV modules are mounted on mechanical solar trackers to optimize power generation throughout the day or seasonally.
Numerous RF antenna designs, with wavelength specific resonant structures, have been implemented including, planar or low-profile antenna. Exemplary designs include patterned metallic, or conductive, micro-strip patch antenna and meta-material surface antennas. Phased array antenna (PAA) configurations have been used to enhance performance or to enable directional beam steering. Fractal designs have been used to enable multi-frequency operation. RF systems have also been integrated with other electrical systems including PV systems, although due attention should be paid to address potential interference and increased signal noise issues. Standard approaches for electrical isolation and grounding are typically employed to mitigate such issues. RF antenna designs have also been proposed for mobile applications including unmanned aircraft vehicles (UAVs) and mobile phones. However the proposed designs are non-planar or folded.
Systems in which PV cells and RF antennas are combined have been proposed for autonomous, self-powered communication and sensor devices. Typically the PV and RF systems in these applications are either (i) independently positioned on structures without significant integration or (ii) overlaid on top of each other. The latter configurations can have a top layer with a patterned antenna structure which frames a window to underlying PV cells or have an overlaid array of PV cells which are spaced to provide channels to underlying antenna. Each of these approaches gives rise to significant limitations. For instance, the relatively large size and weight of these PV and RF systems may be a significant hindrance for us in or on various types of platforms, especially on aircraft platforms. If the PV and RF systems are overlaid the performance of one system may be compromised by partial shading or shielding by the other. Furthermore PV and RF systems can have different operational directions. That is, PV systems are ideally oriented towards the sun for maximum power generation while RF antennas may need to be oriented towards remote transmitting or receiving systems in order to establish a strong communications link. These directionalities can be conflicting and the problem can be further exacerbated if the integrated system is located on a moving platform such as an individual or vehicle with a separately defined mission path. In the integrated planar approaches noted above, the PV and RF antenna functionalities typically operate through the same face of the article. Such mono-facial operation can be appropriate for terrestrial applications where system orientations for receiving solar illumination and RF communications are generally in upward and lateral directions but are inappropriate for elevated, airborne or space applications where the desired RF communications link orientation can be in the opposite direction to solar illumination.